1. Field of the Invention
The present invention relates to a hybrid balun apparatus and, more particularly, to a hybrid balun apparatus supporting both reception and transmission modes and being advantageous for a high level of integration.
2. Description of the Related Art
In the past, RF baluns and transmission/reception switches (T/R SW) were separately designed or integrated, rather than being designed as a one chip.
RF baluns are divided into an RF balun designed with a passive element and an RF balun designed with an active element.
A passive element commonly uses a structure with a transformer, and structures of actually used transformers are different in designs and variably implemented. Such a passive element has good linearity but with a loss of signal.
An active element is designed with a CMOS transistor to generate differential signals having the same signal size but with a phase difference of 180°, which has a relatively good gain but is disadvantageous in that power is wasted and its linearity is worse than that of the passive element.
Thus, recently, a balun apparatus having a hybrid structure combining a passive element and an active element has been proposed.
FIG. 1 illustrates the prior art hybrid balun apparatus.
As shown in FIG. 1, the prior art hybrid balun apparatus includes a band pass filter (BPF) 10 that filters a frequency band of a signal received via an antenna, a T/R switch 21 that selects a transmission path of a signal, two transformers 22 and 23 positioned at a reception path and a transmission path, respectively, a differential low noise amplifier (LNA) 30 that amplifies a signal transmitted via the transformer 22 positioned at the reception path, and a differential power amplifier (PA) 40 that applies a signal desired to be output, to the transformer 23 positioned at the transmission path.
In a reception mode, a signal input via the antenna passes through the BPF 10 so as to be filtered into a signal of a desired band, which then passes to the transformer 22 through the reception path so as to be input to the differential LNA 30.
Conversely, in a transmission mode, a signal applied via the differential PA 40 passes through the transformer 23 on the transmission path so as to be changed into a single-ended signal, which is then output to the antenna through the T/R switch 22 and the BPF 10.
In this manner, the prior art hybrid balun apparatus supports both the reception mode and the transmission mode by using the two transformers and the single T/R switch.
However, the two transformers provided at the reception path and the transmission path, respectively, occupy a relatively larger area, impeding a high level of integration of the hybrid balun apparatus.
In addition, when the signal passes through the T/R switch, a great deal of loss occurs in the signal, and it is noted that isolation characteristics between the reception path and the transmission path, and the like, are degraded in comparison with the performance of a commercial chip.